Seamless access to modern office tools is one of the most valuable assets for mobile business professionals today. Most corporate information systems and databases can be accessed remotely through the Internet (IP) backbone, but the high bandwidth demand of typical office applications, such as large e-mail attachment downloading, often exceeds the transmission capacity of cellular networks. Mobile professionals are looking for a public wireless access solution that could cover the demand for data-intensive applications and enable smooth online access to corporate data services. Wireless standards, such as IEEE 802.11 and Blue Tooth (BT) are designed to enable mobile devices, such as mobile telephones, laptop computers and personal digital assistants (PDAs) to communicate with each other and a wired Local Area Network (LAN).
Such mobile devices are capable of moving between wireless LANs (WLANs), and some mobile devices can roam between different types of wireless networks (e.g., a WLAN and a cellular mobile telecommunications network). Such transfers typically require establishing a new connection with the new WLAN for the mobile device making the transfer.
These technologies provide for a common attachment approach for different devices, and so enables mobile phones, laptops, and PDAs to be easily networked in the office and in public locations. The IEEE 802.11 (Institute of Electrical & Electronics Engineers) and ETSI (European Telecommunications Standards Institute) HIPERLAN/2, provide a wireless connection function and may be used to support WLAN (wireless LAN) communications.
The IEEE 802.11 Wireless LAN standard focuses on access points on the same subnet. If a mobile device decides to associate itself with a new access point on the same subnet then it uses a series of Associate and Disassociate commands defined within the IEEE 802.11 specification to signal its move from the old to the new access point. If a mobile device transfers to a new subnet, a new secure (WEP) session is typically established between the mobile device and the new access point with a new encryption link.
Some mobile devices also have the capability of moving among different types of wireless communication networks, such as between a WLAN network (Bluetooth or IEEE 802.11, as described above) and a mobile telecommunications network, such as one based on a mobile telephone communication protocol (e.g., CMTS or cellular mobile telephone system, GSM or Global System for Mobile communications, PCS or Personal Communications Services, or UMTS or Universal Mobile Telecommunications System). For example, the mobile device (e.g., laptop computer or PDA) includes communications interfaces (e.g., communications hardware and software) that allow the mobile device to communicate with two (or more) different types of wireless networks. Typically, when the mobile device moves to access a different type of wireless network, the current communication session with the current wireless network terminates, and the mobile device establishes a new communication session (new communication) with the newly accessed wireless network.
To be truly effective, mobile users must be able to move their mobile devices freely from location to location. For example, users must be able to move their mobile devices from the office to their own conference room to the airport lounge to their client's conference room, while maintaining access to the some set of resources without manually registering anew in each location. They should also be able to send and receive messages and voice calls, wherever they are located. Connection servers, such as routers, WLAN gateways, and security servers, should be able to handle a mobile device that moves its connection to the network from access point to access point, from public to private networks, or from one wireless network system to a different type of wireless network system.
U.S. patent application Ser. No. 20020136226 shows a system for enabling seamless roaming of mobile devices among wireless networks. A network gateway manages roaming of a mobile device between heterogenous network systems. The network gateway obtains an access identifier from another heterogenous network system so the mobile device can roam to the other heterogenous network system while maintaining its connection to the home network gateway for the mobile device.
Coupling of WLANs and Public Land Mobile Networks (PLMN) systems can be implemented in different ways. 3GPP defines six stages of coupling with an increasing level of interworking.
The scenarios range from Open Coupling (level 1, basically constituting two separate access systems with common billing only) over Loose Coupling (level 2 and 3, additionally common Authentication, Authorization, and Accounting (AAA) services) to Tight (level 4 and 5) and Very Tight Coupling (level 5 and 6). Several field trials currently are implementing and testing the Open and Loose approach.
Further an approach for tight coupling has been suggested wherein the access points of the WLAN are directly coupled to the SGSN of the core network by means of an interworking unit (IWU). To date the prior art is silent regarding approaches for very tight coupling.
It is therefore an object of the present invention to provide and improved interface unit/interworking unit enabling very tight coupling of 3GPP/UMTS and WLAN-type systems. Further the invention aims to provide a corresponding hybrid telecommunication system and telecommunication method.